Synergistic sensitization of photographic silver halide emulsions



United States Patent New Jersey No Drawing. Filed Oct. 26, 1961, Ser. No. 147,766 6 Claims. (Cl. 96-408) This invention relates to synergistic combinations of various sulfur-containing compounds for increasing the speed of photographic silver halide emulsions.

Photographic silver halide emulsions can be chemically sensitized with a variety of compounds in order to increase the speed, and frequently the gamma, of the emulsions, as opposed to spectral or optical sensitization wherein the range of spectral sensitivity is increased. Perhaps the most common of all chemical sensitization is sulfur sensitization, a phenomenon which is generally believed to be due to the chemical reaction of the sensitizer with the silver halide to form silver sulfide specks in or on the surface of the silver halide crystals or grains. Such sulfur compounds are known as sulfur sensitizers and their activity is believed to be due to the presence of a labile sulfur atom. See Mees, The Theory of the Photographic Process, 1954, the Macmillan Company, page 90, et seq.

Another common type of chemical sensitization results in the formation of small specks of metallic silver or another noble metal in or on the silver halide crystal or grain. Where silver is formed in or on the crystal, this is apparently the result of partial reduction of the silver halide to metallic silver, and the chemical sensitizers exhibiting this property are known as reduction sensitizers (see Lowe, Jones and Roberts, Fundamental Mechanism of Photographic Sensitivity (1951), pages 112425). Where the noble metal introduced on or in the silver halide crystal is gold, this is commonly known as gold sensitization. The effects of these types of sensitization are generally additive, although this may not always be the case, for the effect is somewhat dependent upon the compounds used as sensitizers and their chemical activity under a given set of emulsion conditions.

Still another type of sensitization results from treatment of the silver halide emulsions with derivatives of certain alkylene oxides, such as ethylene oxide. This particular type of sensitization is generally not called chemical sensitization, since there has been little or no evidence that such compounds react with the silver halide grain. Rather, the effect of these types of sensitizers is believed to be a consequence of development phenomena, and the mechanism of such sensitization is rather incompletely understood.

The present invention is concerned with a means of synergistically increasing the speed obtainable with sulfur sensitizers by adding to photographic silver halide emulsions compounds which have no observable effect in increasing the speed of the emulsions. Actually, the compounds of my invention which have a useful synergistic effect upon sulfur sensitizers, i.e., compounds which contain a labile sulfur atom, have primarily been recognized in the prior art as antifoggant or stabilizing compounds. Accordingly, it was quite unexpected to find that these antifoggant compounds should be usefully employed to increase further the speed obtainable with sulfur sensitizers.

It is, therefore, an object of my invention to provide 3,144,336 Patented Aug. 11, 1964 gistically increasing the speed of photographic silver halide emulsions which have been sensitized with various types of sulfur sensitizers. Other objects will become apparent from a consideration of the following description and examples.

I have found that organic sulfinic acids, or their watersoluble salts, can be used together with sulfur sensitizers, i.e., compounds containing a labile sulfur atom, to effectively increase the speed of various photographic silver halide emulsions. The sulfinic acids or their water-soluble salts can be used in combination with various types of sulfur sensitizers, including organic and inorganic sulfur sensitizers.

The sulfinic acids, or their water-soluble salts, which can effectively be used in my invention include aliphatic, aromatic, hydroaromatic or heterocyclic sulfinic acids and salts, such as methanesulfinic acid, methanedisulfinic acid, ethanesulfinic acid, benzenesulfinic acid, chlorobenzene sulfinic acid, p-toluenesulfinic acid, p-anisolsulfinic acid p-acetanilidesulfinic acid, salicylicsulfinic acid, m-benzenesulfinic acid, fi-naphthalenesulfinic acid, cyclohexanesufinic acid, thiophenesulfinic acid, etc., as well as their water-soluble salts, such as sodium, potassium, ammonium, pyridinium, triethanolammonium, etc.

The sulfinic acids, or their water-soluble salts, are generally added to the silver halide emulsions useful in my invention in substantially neutral aqueous solutions, although the acids as such can frequently be added at low concentrations in their aqueous solutions to the emulsion. The concentrations of these compounds can be varied depending upon the particular silver halide emulsion in question, the concentration of silver halide, the vehicle in the emulsion (either gelatin or some other water-permeable hydrophilic colloid, such as polyvinyl alcohol, collagen, albumin, etc.), etc. In general, I have found that useful efiects can be obtained when the concentration varies over a range of from about 0.01 to about 10 grams per mole of silver halide, although lower or higher concentrations can advantageously be employed.

The emulsions useful in my invention can be sensitized with a variety of the labile sulfur compounds known to those skilled in the art of photography. Such sulfur sensitizers can be inorganic compounds, such as sodium thiosulfate, potassium thiosulfate, ammonium thiosulfate, etc., or organic compounds, such as allylthiocarbamide, dithioformic acids or water-soluble salts thereof (e.g., sodium, potassium, etc.), or derivatives thereof, such as cyanodithioformic acid or water-soluble salts thereof, such as sodium, potassium, ammonium, etc.), dithiocarbamic acids or water-soluble salts thereof (e.g., sodium, potassium, ammonium, etc.), i.e., compounds represented by the following general formula:

wherein R represents a hydrogen atom, an alkyl radical, such as methyl, ethyl, fi-hydroxyethyl, propyl, isopropyl, butyl, etc., or an aryl radical, such as phenyl, p-tolyl, chlorophenyl, etc. (e.g., a monocyclic aryl radical of the benzene series containing from 6 to 7 carbon atoms) and M represents a hydrogen atom or an atom or radical imparting water solubility, such as sodium, potassium, am-

monium, triethanolammonium, etc; or disulfides, such as forrnamidinedisulfides, xanthyldisulfides, thiuramdisulfides, acyldisulfides, etc., including compounds represented by the following general formula:

wherein R represents an alkoxyl radical, such as methoxyl, ethoxyl, propoxyl, etc., an alkyl radical, such as methyl, ethyl, propyl, butyl, etc., an aryl radical, such as phenyl, p-tolyl, chlorophenyl, etc., a dialkylamino radical such as dimethylamino, diethylamino, etc. and Q represents an oxygen atom, a sulfur or an imino radical. Other sulfur sensitizers can likewise be employed to advantage, and it is to be understood that the sulfur sensitizers commonly known to the art can be used in my invention. Gen erally, the silver halide emulsions useful in my invention are sensitized to their optimum or near optimum with a labile sulfur compound, an aqueous solution of the sulfinic acid compound is then added and the emulsion is then digested for a short time prior to coating. However, the order of addition of the sulfinic acid compound and the sulfur sensitizer can be reversed if it is desired.

The photographic emulsions used in my invention are generally of the developing-out type.

The emulsions used in my invention can be additionally sensitized with other sensitizing materials, such as the salts of noble metals, such as gold, ruthenium, rhodium, palladium, iridium, platinum, etc. Typical gold salts which can be used in sensitizing the emulsions of my invention are those described in Waller et al. U.S. Patent 2,399,083, issued April 23, 1946, and Damschroder et al. U.S. Patent 2,642,361, issued June 16, 1953, etc. Typical gold sensitizers include potassium chloroaurite, potassium aurithiocyanate, auric trichloride, potassium chloroaurate, etc.

The following examples will serve to illustrate the manner whereby I obtain a synergistic sensitization of photographic silver halide emulsions.

Coarse-grained photographic gelatino-silver-bromiodide emulsions were employed in Examples 1 to 3. These emulsions had not been previously chemically sensitized or spectrally sensitized. Each of the emulsions was then chemically sensitized with a different sulfur sensitizer as identified in Tables A-C below and in the concentrations given in these tables. The emulsions were then divided into two batches and one batch of each emulsion was treated with 9 grams per mole of silver of sodium p-toluenesulfinate. Each of the batches was then digested for a few minutes at a temperature of from about 50 to 55 C. and coated on ordinary cellulose acetate film support and dried. Each of the film samples was exposed on an Eastman Type Ib Sensitometer to tungsten illumination and developed for a few minutes in a developer having the following composition:

G. N-methyl-p-aminophenol sulfate (Elon) 2.0 Sodium sulfite (anhydrous) 90 Hydroquinone 8.0 Sodium carbonate monohydrate 52.5 Potassium bromide 5.0

Water to make one liter.

The developed coatings were then fixed, washed and dried in the usual manner. The relative speed for each of the coatings was then measured at a density of 0.3 density units above fog. The results obtained are summarized in the following tables. No speed data are given as to the effect of sodium p-toluene-sulfinate alone, inasmuch as it was found that this compound was not effective alone in increasing speed (as recognized in the prior art). Since the film coatings were made from a number of different emulsions, the relative speed of one coating may not necessarily correspond to that of another coating, and hence, reliable comparisons of the relative speed of one Example 1 Table A Relative Speed Without Sulfiuate Relative Coating Series Sensitizer (g./m0le Ag) Sulfmate Sodium Thiosultate (018).- Sodium cyanodithiol'ormate Example 2 Table B Relative Coating Series Sensitizer (g./mole Ag) Without;

(c) N-butyldithiocarbamie acid ammonium salt (.009).

Benzoyl disulfide (.003).

Example 3 Table 0 Emulsion similar to Example 2 sensitized except it has been gold Relative Speed Without With Coating Series Seusitizer (g./mole Ag) (:2) N-ethyldithiocflrbamic acid 100 23% ammonium salt (.009).

EXAMPLE 4 An ordinary photographic gelatino-silver-bromide emulsion, which had not been chemically or spectrally sensitized, was first modified by adding thereto .009 gram per mole of silver halide of the ammonium salt of N-ethyldithiocarbamic acid. The emulsion was then divided into four batches and three of the batches were then modified by adding thereto a sulfinic acid compound as identified in the following table and at the concentration shown in the table. The four batches were digested for a few minutes at about 55 C. and then coated on ordinary cellulose acetate film support and dried. The coatings were then exposed, developed, fixed, washed and dried as described above with respect to Examples 1 to 3. The speed figures were obtained as described above, measurement being made at 0.3 density units above fog. The following results were obtained.

Table D Batch I Sulfinate (g./mole Ag) I Speed Gamma Fog (I) Control sulfinate) 100 Sodium -tolueue-sulfinate (0.3)...

Sodium enzeue sulfinate (0.9)..-.

p-Acetamido benzene sulfiuic neu- 132 tralizerl (0.9).

bromiodide, silver chlorobromide, silver chlorobromiodide, etc. These emulsions can be used in various types of photographic products, such as those intended for primarily black-and-White photography for the production of a negative or positive image, as well as those intended for color photography. When used in color photography, they can be employed in emulsions which have been spectrally sensitized to a given region of the spectrum as Well as emulsions which have not been spectrally sensitized. The emulsions can contain the usual addenda for modifying the properties of the emulsions, including color couplers for the production of various types of color images, such as phenolic couplers for production of the cyan image, pyrazolone type couplers for the production of a magenta image or open-chain ketomethylene compounds for the production of a yellow image. These emulsions can contain the usual addenda, such as hardeners, antifoggants, tone-modifying compounds, etc. The emulsions can be used in X-ray photography or in more conventional processes of the above types.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

What I claim and desire secured by Letters Patent of the United States is:

1. A photographic silver halide emulsion sensitized with a sulfur sensitizer selected from the class consisting of an alkali metal thiosulfate, a compound represented by the following general formula:

and a compound represented by the following general formula:

( R1-os-s-o R,

wherein R represents a member selected from the class consisting of a hydrogen atom, an alkyl radical and an aryl radical, R represents a member selected from the class consisting of an allcoxyl radical, an alkyl radical, an aryl radical and a dialkylamino radical, M represents a member selected from the class consisting of a hydrogen atom and a radical imparting a water-solubility to said depicted compound (A) and Q represents a member selected from the class consisting of an oxygen atom, a sulfur atom and an imino radical, said photographic silver halide emulsion containing a compound selected from the class consisting of methane suliinic acid, methane disulfinic acid, ethane sulfinic acid, benzene sulfinic acid, chlorobenzene sulfinic acid, p-toluene sulfinic acid, p-anisol sulfinic acid, p-acetanilide sulfinic acid, salicylic sulfinic acid, m-benze11e sulfinic acid, B-naphthalene sulfinic acid, cyciohexane sulfinic acid, thiophene suliinic acid, and water-soluble salts of said sulfinic acids.

2. A photographic silver halide emulsion sensitized with sodium thiosulfate and sodium p-toluenesulfinate.

3. A photographic silver halide emulsion sensitized with the sodium salt of cyanodithioformic acid and sodium p-toluenesulfinate.

4. A photographic silver halide emulsion sensitized with N-butyldithiocarbamic acid ammonium salt and sodium p-toluenesulfinate.

5. A photographic silver halide emulsion sensitized with benzoylclisulfide and sodium p-toluenesulfinate.

6. A photographic silver halide emulsion sensitized with N-ethyldithiocarbamic acid ammonium salt and sodium p-toluenesulfinate.

References tiited in the file of this patent UNITED STATES PATENTS 1,574,944 Sheppard Mar. 2, 1926 1,678,832 Sheppard July 31, 1928 2,057,764 Brunken Oct. 20, 1936 2,540,085 Baldsiefen Feb. 6, 1951 2,759,821 Jones et a1. Aug. 21, 1956 2,983,610 Allen et al. May 9, 1961 3,017,270 Tegillus et al. Jan. 16, 1962 

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION SENSITIZED WITH A SULFUR SENSITIZER SELECTED FROM THE CLASS CONSISTING OF AN ALKALI METAL THIOSULFATE, A COMPOUND REPRESENTED BY THE FOLLOWING GENERAL FORMULA: 